The rumours are that the M chip will be released for the 125i and 135i soon and that could take the 125i from 163kw to over the 200kw and give a sub 5.
The 125i is quick as it is. I think the real 0-100 time is closer to a flat 6.00

Is the rumour based on the M performance part or after market?? 200kw will be great!

You will not be disappointed with the 125i... I picked up a manual M sport and it is a fun to drive. I would at times make up an excuses to my wife (need to buy milk and bread in the middle of the night) so I can take the car out for a drive